Phobos: Regolith and ejecta blocks investigated with Mars Orbiter Camera images

Thomas, P. C.; Veverka, J.; Sullivan, Robert; Simonelli, D. P.; Malin, M. C.; Caplinger, M. A.; Hartmann, W. K.; James, P. B.

doi:10.1029/1999je001204

Cited by 77 publications

(45 citation statements)

References 34 publications

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“…The morphology of the pitted grooves and troughs seen on Eros is not as crisp and well defmed as that observed on Phobos (Thomas et al, 2000) indicating that the regolith on Eros is thicker than that on Phobos. In a comparison of the morphology of Deimos and Phobos Thomas et at.…”

Section: Discussionmentioning

confidence: 81%

“…No analogous ponded deposits have been identified on Phobos in published work (Thomas et a!., 2000) and our examination of Mars orbiter camera (MOC) images ofPhobos have revealed no planar or flat floored craters similar to ponds found on Eros. Lunar crater morphologies were cataloged from high-resolution Lunar Orbiter images (1 m/pixel and better) in a series ofpapers (see discussion above; Quaide, 1967, 1968;Quaide and Oberbeck, 1968).…”

mentioning

confidence: 93%

“…6-8) in Eros craters suggests a well-mixed regolith with properties changing gradually with depth to many meters to tens of meters everywhere on the asteroid. We note that Thomas et al (2000) identified a few craters on Phobos that may indicate a lunar-like strength-interface (Fig. 7).…”

Section: Regolithmentioning

confidence: 99%

“…The Phobos data (from Thomas, 1998;Thomas et al, 2000) include a global data set (>700 m diameter), and some local data at good viewing down to pixel scales of -4 ill. The Phobos and Eros crater densities between 30 and 200 m are similar except for the steep topography (slopes _20°) within Stickney crater, which has a substantially lower crater density.…”

Section: Impact Craters Crater Densitiesmentioning

confidence: 99%

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The geology of 433 Eros

Robinson

Thomas

Veverka

et al. 2002

Meteorit & Planetary Scien

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Abstract-The global high-resolution imaging of asteroid 433 Eros by the Near-Earth Asteroid Rendezvous (NEAR) Shoemaker spacecraft has made it possible to develop the first comprehensive picture of the geology of a small S-type asteroid. Eros displays a variety of surface features, and evidence of a substantial regolith. Large scale facets, grooves, and ridges indicate the presence of at least one global planar structure. Directional and superposition relations of smaller structural features suggest that fracturing has occurred throughout the object. As with other small objects, impact craters dominate the overall shape as well as the small-scale topography of Eros. Depth/diameter ratios of craters on Eros average -0.13, but the freshest craters approach lunar values of -0.2. Ejecta block production from craters is highly variable; the majority oflarge blocks appear to have originated from one 7.6 km crater (Shoemaker). The interior morphology of craters does not reveal the influence of discrete mechanical boundaries at depth in the manner of craters formed on lunar mare regolith and on some parts of Phobos. This lack of mechanical boundaries, and the abundant evidence of regolith in nearly every high-resolution image, suggests a gradation in the porosity and fracturing with depth. The density of small craters is deficient at sizes below -200 m relative to predicted slopes of empirical saturation. This characteristic, which is also found on parts ofPhobos and lunar highland areas, probably results from the efficient obliteration of small craters on a body with significant topographic slopes and a thick regolith. Eros displays a variety ofregolith features, such as debris aprons, fine-grained "ponded" deposits, talus cones, and bright and dark streamers on steep slopes indicative ofefficient downslope movement ofregolith. These processes serve to mix materials in the upper loose fragmental portion ofthe asteroid (regolith). In the instance of "ponded" materials and crater wall deposits, there is evidence of processes that segregate finer materials into discrete deposits. The NEAR observations have shown us that surface processes on small asteroids can be very complex and result in a wide variety of morphologic features and landforms that today seem exotic. Future missions to comets and asteroids will surely reveal still as yet unseen processes as well as give context to those discovered by the NEAR Shoemaker spacecraft.

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Section: Discussionmentioning

confidence: 81%

mentioning

confidence: 93%

Section: Regolithmentioning

confidence: 99%

Section: Impact Craters Crater Densitiesmentioning

confidence: 99%

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The geology of 433 Eros

Robinson

Thomas

Veverka

et al. 2002

Meteorit & Planetary Scien

Self Cite

155

140

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“…1996 MOC imagery of Phobos (Thomas et al, 2000); low-res thermal IR coverage by TES (Roush and Hogan, 2000); ranging by MOLA (≥265 km range) (Banerdt and Neumann, 1999); more observations were carried out during 2003.…”

Section: Mars Global Surveyor (Mgs)mentioning

confidence: 99%

Mars Phobos and Deimos Survey (M-PADS) – A martian Moons orbiter and Phobos lander

Ball

Price

Walker

et al. 2009

Advances in Space Research

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We describe a Mars 'Micro Mission' for detailed study of the martian satellites Phobos and Deimos. The mission involves two ~330 kg spacecraft equipped with solar electric propulsion to reach Mars orbit. The two spacecraft are stacked for launch: an orbiter for remote investigation of the moons and in situ studies of their environment in Mars orbit, and another carrying a lander for in situ measurements on the surface of Phobos (or alternatively Deimos). Phobos and Deimos remain only partially studied, and Deimos less well than Phobos. Mars has almost always been the primary mission objective, while the more dedicated Phobos project (1988-89) failed to realise its full potential. Many questions remain concerning the moons' origins, evolution, physical nature and composition. Current missions, such as Mars Express, are extending our knowledge of Phobos in some areas but largely neglect Deimos. The objectives of M-PADS focus on: origins and evolution, interactions with Mars, volatiles and interiors, surface features, and differences. The consequent measurement requirements imply both landed and remote sensing payloads. M-PADS is expected to accommodate a 60 kg orbital payload and a 16 kg lander payload. M-PADS resulted from a BNSC-funded study carried out in 2003 to define candidate Mars Micro Mission concepts for ESA's Aurora programme.

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Impact fragmentation of Lonar Crater, India: Implications for impact cratering processes in basalt

et al. 2014

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Impact fragmentation is an energetic process that has affected all planetary bodies. To understand its effects in basalt, we studied Lonar Crater, which is a rare terrestrial simple impact crater in basalt and analogues to kilometer-scale simple craters on Mars. The Lonar ejecta consists of basaltic fragments with sizes ranging from silt to boulder. The cumulative size and mass frequency distributions of these fragments show variation of power index for different size ranges, suggesting simple and complex fragmentation. The general shape of the fragments is compact, platy, bladed, and elongated with an average edge angle of 100°. The size distribution of cobble-to boulder-sized fragments is similar to the fracture spacing distribution in the upper crater wall, indicating the provenance of those large fragments. Its consistency with a theoretical spallation model suggests that the large fragments were ejected from near surface of the target, whereas the small fragments from deeper level. The petrophysical properties of the ejecta fragments reflect the geophysical heterogeneity in the target basalt that significantly reduced the original size of spall fragments. The presence of Fe/Mg phyllosilicates (smectites) both in the ejecta and wall indicates the role of impact in excavating the phyllosilicates from the interior of basaltic target affected by aqueous alteration. The seismic images reveal a thickness variation in the ejecta blanket, segregation of boulders, fractures, and faults in the bedrock beneath the crater rim. The fracturing, fragmentation, and fluvial degradation of Lonar Crater have important implications for Mars.

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Phobos: Regolith and ejecta blocks investigated with Mars Orbiter Camera images

Cited by 77 publications

References 34 publications

The geology of 433 Eros

The geology of 433 Eros

Mars Phobos and Deimos Survey (M-PADS) – A martian Moons orbiter and Phobos lander

Impact fragmentation of Lonar Crater, India: Implications for impact cratering processes in basalt

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